The Sunfire Fusilier - Plasma Gunner Build
 Skitarii Build - Warhammer 40k: Darktide 

Plasma Gunner Backliner -  "The sun does not chase its target. Neither do I."

Doctrina Solaris — sanctioned by the Sacred Forge as an offering of controlled combustion

The Plasma Gun - A righteous piece of radiant artillery, a crit machine thanks to Servo-Sinew Surge Piercing Sight and Gets Hot!. Light spam is still mainly the best way to use it thanks to Blaze Away, and dump stat is an even split between thermal resistance and charge rate, allowing you to get 1 shot off extra before overheating that you normally wouldn't with a pure thermal resistance dump stat. Gunsmith is mandatory so you never have the reload that baby; the rite must not be interrupted by mechanical delay; the sun does not pause to reload.

Sunfire Auto-Aim - Your Doctrine made manifest, the weapon's own cogitator surpassing even a Veteran's aim when brought to bear on Crushers and bosses. Still best to only shoot till overheat, then swap to sword, as the drain is NOT paused when cooling down the gun, unlike reloading. No problem; most threats find resolution within six to eight sanctified weakspot discharges to the cranium.

Personal Bubble Shield - The Omnissiah's own grace, rendered cooldown-only by decree Sacred Fatsharks most recent revision. Great for revives and while shooting in Advanced Combat Doctrines, probably still worse than servo skull, and that is still an option here, but this feels more thematic and improves your niche as the anti-gunner on the team. 

Power Falchion - The secondary rite, drawn when the primary instrument requires its cooling period. Light spam while energised will deal with most hordes, with the occasional heavy for the armour too close to shoot. I like blessings that apply even when not empowered, like Cranial Grounding, and Wrath means no need for nodes such as Adaptive Combat Calibrationor Shockline Breach Protocol. 

Flensing - The best option keystone for this rite due to always shooting at max power with Enhanced Capacitance Protocols and the crit focus of Servo-Sinew Surge. Cooldown is rarely an issue with Advanced Combat Doctrines ammo is so the other keystones are largely unnecessary. The sun need not hasten. It needs only to endure until the purge is complete.